I may be biased because I'm insensible to visual art. But the valuation of those seems like a scam even without the Tax evasion scheme.
TLDW:
1-Buy collection at low price from artiste
2-increase interest in said artist:
paid article pay Gallery to promote artist
Sell some piece at auction and buy it yourself at an inflated price. Allowed by Secrecy in auction
3- profit:
give some overpriced (by auction) piece to museum for massive tax evasion all you collection is now overvalued based on the auction price
All actors are incentivize to participate in the scam:
Gallery and auction house get paid Museum get free art
Artist get reconnaissance